Substantially more health plans on the federal insurance marketplaces require consumers next year to pay a hefty portion of the cost of the most expensive drugs, changes that analysts say are intended to deter persistently ill patients from choosing their policies. The class of medicines known as specialty drugs treat chronic illnesses such as multiple sclerosis, rheumatoid arthritis, HIV, hemophilia, some cancers, and hepatitis C. Some medicines can cost $10,000 a month. Even a small cost-sharing requirement means patients could have to come up with thousands of dollars to get the medicines.

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